Conventionally, an imaging apparatus for diagnosis has been widely used in order to perform diagnosis on arteriosclerosis, to perform preoperative diagnosis before endovascular therapy which uses a high-function catheter such as a balloon catheter or a stent, or to verify results after surgery.
The imaging apparatus for diagnosis includes an intravascular ultrasound (IVUS) device, an optical coherence tomography (OCT) device, and the like, which have different respective characteristics. For example, ultrasound reaches a relatively deep location of body tissues, and so an IVUS cross-sectional image is conveniently used in diagnosing tissues at a relatively deep location. On the other hand, light does not have a comparable reachable distance to ultrasound, but can be used to acquire higher-resolution images. Accordingly, although an optical cross-sectional image allows diagnosis only for tissues at a relatively shallow location, the image obtained thereby will have much higher resolution compared to the ultrasound. For the above-described reasons, a technique is known in which both an IVUS function and an OCT function are provided so as to display a composite image by setting a light-reachable limit to a boundary in an optical cross-sectional image and by employing the optical cross-sectional image on the inside from the boundary and an ultrasound cross-sectional image on the outside from the boundary, for example, as disclosed in Japanese Patent No. 3772002, U.S. Pat. No. 7,935,060, JP-T-2010-516304, and JP-A-2005-095624.
In addition, with the utilization of such an imaging apparatus for diagnosis, it is also possible to understand attribute classification and distribution of vascular tissues. For example, JP-A-2014-97417 discloses a technique of analyzing data obtained through the OCT function so as to classify a vascular cross-sectional image into body regions of Calcification, Fibrosis, and Lipid. In addition, Japanese Patent No. 4933045 and U.S. Pat. No. 6,200,268 each disclose a technique of similarly classifying body tissues, based on data obtained through the IVUS function.